Lecture 1.1: Cell Ultrastructure

Question 1

Nucleus

Answer 1

Contains DNA

Contains Heterochromatin as well as Euchromatin

Question 2

Nucleolus

Answer 2

An area on highly condensed DNA within the nucleus

Question 3

Heterochromatin

Answer 3

Densely packed DNA

Not actively transcibed for RNA synthesis

Question 4

Euchromatin

Answer 4

Less condensed DNA

Thus accessible for RNA synthesis

Question 5

Nuclear Envelope

Answer 5

Double membrane

Contains nuclear pores (to allow mRNA to leave nucleus and reach free ribosomes or RER ribosomes)

Question 6

Rough Endoplasmic Reticulum

Answer 6

Interconnecting membranes, vesicles and cisternae

Has ribosomes attached to outer surface for protein synthesis

Is itself responsible for protein modification, packaging and quality control

Question 7

Ribosomes

Answer 7

Made of 60S and 40S subunits to make an overall 80S ribosome

They are responsible for the protein synthesis within cells

Question 8

What is ultimate fate of proteins synthesises by free ribosomes?

Answer 8

They remain in cytosol or are incorporated into the nucleus, mitochondria and peroxisomes

Question 9

What is ultimate fate of proteins synthesises by RER ribosomes?

Answer 9

They are processes, packaged, modified and exported (extracellular) via the Golgi

Question 10

Smooth Endoplasmic Reticulum

Answer 10

Interconnecting membranes, vesicles and cisternae

Involved in lipid synthesis, steroid production, calcium storage (muscles) and intracellular transport

Question 11

Golgi Apparatus

Answer 11

Saucer shaped stacks of cisternae

Vesicles from ER fuse with cis (convex) face of Golgi

Function to sort, package, modify proteins and lipids

Vesicles containing different lipids/proteins leave trans (concave) face of Golgi and are destined for lysosome assembly or secretion

Question 12

Secretory Vesicles

Answer 12

These often condense into secretory granules and release their contents at the cell surface via exocytosis

Question 13

Lysosomes

Answer 13

Produced at Golgi (Primary lysosomes), diverse in shape

Contain lysozymes (acid hydrolases at pH 5) to hydrolyse residual bodies in cell

Lysosomal membrane proteins are highly glycosylated for protection from these digestive enzymes

Question 14

Lysosomal Storage Disorders (LSDs)

Answer 14

Defects in hydrolytic enzymes

Leads to accumulation of residual bodies as substrates not digested

Can result in diseases such as Tays-Sachs, Hurler syndrome…etc

Question 15

Peroxisomes

Answer 15

Roughly spherical, granular matrix, single membrane

Self replicating but no genome of their own

They detoxify cells (present especially in kidney tubules and liver parenchymal cells to detoxify from toxic molecules in bloodstream)

Major sites of oxygen use and hydrogen peroxide production

RH₂ + O₂ –> R + H₂O₂

Catalase uses this H₂O₂ to oxidise other substrates e.g. alcohol, formic acid…etc

Question 16

Mitochondria

Answer 16

Spherical/ Elongated Oval

Double membrane, inner membrane folded into cristae the space between is called the matrix

Can divide autonomously (have own genetic information)

Primary function is generation of ATP via respiration, main substrates are glucose and fatty acids

Links and Krebs in matrix

Oxidative Phosphorylation in cristae

Question 17

Cytoskeleton

Answer 17

Responsible for maintaining/ changing cell shape

Provides structural support and means of movement for plasma membrane and organelles

Made of:
a) Microfilaments
b) Intermediate filaments
c) Microtubules

Question 18

Microfilaments

Answer 18

5nm diameter

2 strings of actin twisted together

Associated with ATP

Can assemble and dissociate (are dynamic)

Question 19

Intermediate Filaments

Answer 19

Not dynamic

10-12nm diameter

Common in nerve, neuroglial and epithelial cells

Question 20

Microtubules